Smartphones or tablet PCs are widely used in recent years, and development of technology for a contact location measuring device embedded therein is ongoing. The smartphones or tablet PCs are mostly provided with a touch screen, and users may indicate specific coordinates of the touch screen using a finger or a stylus pen. The user may input a specific signal to the smartphone by indicating specific coordinates of the touch screen.
The touch screen may operate based on an electric method, an infrared ray method, and a ultrasonic method, and examples of the touch screen operated in the electric operating method include a resistive touch screen (R-type touch screen) and a capacitive touch screen (C-type touch screen).
In the related art, the R-type touch screen, which can recognize a finger and a stylus pen of a user simultaneously, was popularly used. However, the R-type touch screen has a problem of reflection caused by an air layer formed between ITO layers.
Therefore, the C-type touch screen is increasingly used in recent years. The C-type touch screen is a touch screen which operates by detecting a difference in capacitance of a transparent electrode caused by contact with an object.
Such a C-type touch screen has a trade-off relationship between receive sensitivity of a sensor and a driving time. That is, in order to enhance the receive sensitivity of the sensor, the driving time should increase. However, there is a problem that the increase in the driving time may cause a sensing speed of the sensor to be reduced.
In order to solve this problem, a recent method applies driving signals corresponding to different digital codes to a plurality of driving electrodes, simultaneously, and then extracting location information by decoding response signals. In this case, the digital code applied to each channel is mutually orthogonal signals, and thus a response signal regarding a specific channel can be easily decoded and extracted from reception signals where responses in the plurality of channels are mixed. That is, compared to a sequence driving method, this method has a long driving time for a single channel and thus can enhance receive sensitivity of a sensor.
However, since the related-art method generates a plurality of driving signals using the Hadamard matrices, the first digital code applied to the plurality of channels has the same value. Therefore, a signal Vt1 received in the first section has a very great value compared to signals Vt2-Vtn received in the other sections, and there is a tight limit to configuring a receiving end in order to detect signals in all sections including the first section.
That is, in order to detect a minute change in capacitance of a driving electrode, the level of a signal which can be received at a reception circuit should be set to be low, but, in order to receive a great reception signal Vt1 in the first section, the reception circuit should have a great dynamic range.